Hi,
Thanks for posting your query.

The lump you are feeling behind your shoulder is in all probability a benign lesion. If the lump is movable without any skin changes then it will be very reassuring. The possible causes may be a lipoma or neurofibroma. These are benign tumours and do not usually cause problems even if left alone.

The possibility of a sarcoma (malignant) is low if it is freely movable and not hard.

However, the most important thing at this stage is to get it examined by a physician and assess the need for biopsy. If it is clearly benign, then biopsy or needle aspiration is not required. You may also require radiological imaging (CT scan or MRI), if the need is felt by your physician.

I hope I have answered your query. Please accept my answer f you have no further follow up queries.

Regards.

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